Conventionally, in cutting inserts mounted on an indexable rotary cutting tool, there is the type of cutting insert to have a cutting edge formed on each of an upper surface and a lower surface which are two end surfaces of the cutting insert. This type of cutting insert includes, for example, a cutting insert that can be mounted on a tool body in a manner such that the upper surface and the lower surface are exchanged by flipping it. Furthermore, this cutting insert has cutting edges of which number is greater than that of a single-sided type. For this reason, the double-sided type of cutting insert as described above is economical.
Patent Literature 1 discloses one example of the double-sided type of cutting insert includes cutting edges having the same shape formed on the upper and lower surfaces. This cutting insert is basically configured to include an upper surface and a lower surface, each of which has a substantially quadrilateral shape, and a peripheral side surface connecting to these surfaces. A corner cutting edge is formed on each of a pair of corners disposed at diagonal positions on the upper surface. A major cutting edge is formed on a longer ridgeline portion extending from a corner having a corner cutting edge formed thereat, and a minor cutting edge is formed on a shorter ridgeline portion extending from this corner in a direction different from that of the longer ridgeline portion. The major cutting edge is longer than the minor cutting edge. Similarly, the corner cutting edge, the major cutting edge, and the minor cutting edge are formed on the lower surface. Furthermore, in this cutting insert four corner cutting edges are disposed on the upper and lower surfaces in a manner such that a diagonal line which connects the corner cutting edges diagonally located on the lower surface intersects with a diagonal line which connects the corner cutting edges on the upper surface. As described above, in this cutting insert four corners, each of which can be used in cutting work, are disposed so that the corner cutting edges on the upper surface are not aligned with the corner cutting edges on the lower surface in the thickness direction of the cutting insert. When the cutting edge on the upper surface side is used for cutting, the cutting insert is mounted on the tool body so that the lower surface is brought into abutment with a bottom wall surface of an insert seat of the tool body. On the other hand, when the cutting edge on the lower surface side is used for cutting, the cutting insert is mounted on the tool body so that the upper surface is brought into abutment with the bottom wall surface of the insert seat of the tool body.